The long-term objectives of this research proposal are to investigate current concepts of lipid transport in the intact animal, in isolated cells and between subcellular components. The deposition of excess lipid in tissues is accompanied by cellular malfunctions that result in diseases such as atherosclerosis. We intend to continue current work at three levels: 1) the study of membrane lipid organization in cell membranes and of methods to alter membrane lipid composition and its effect on membrane-bound enzymes, 2) the mechanisms whereby diet causes hyperlipidemia animals, and 3) the mechanisms whereby cholesterol is absorbed from the intestine. Future studies will include attempts to alter membrane lipid compositions by the use of lipid transfer proteins first recognized and isolated in our laboratory. It will be possible to alter the fally acid saturation as well as polar group composition of membrane lipids and subsequently study the effect of these alterations on enzymes such as adenyl cyclase, acylCoA:Cholesterol Acyltransferase and glucose-6-phosphatase as examples. The effects of lipid substitutions on intestinal cell brush border preparations will allow the study of dependence of lipid transport phenomena in the intestine on membrane composition. In the intact rabbit we will utilize labeled cholesterol and retinol to measure the mechanism of absorption of these lipids from the intestine and their subsequent transport to the bloodstream and various tissues. Lipoprotein lipid and polypeptide analysis coupled with isotopic studies will be employed to trace the origins of plasma cholesterol in rabbits subjected to high cholesterol and to animal protein diets.